1. Field of the Invention
The present invention relates to universal serial bus (USB) devices. More particularly, the present invention relates to USB devices having unique power sharing capabilities.
2. General Background of the Invention
Normally, USB host devices provide power to USB client devices. The USB specification does not entertain the option of the USB client detecting and providing power to the host device.
USB interface version 2.0 specifies that USB host devices be able to provide power to a USB client device. Self-powered USB client devices typically use the power pin to detect the presence of a host USB device.
A USB host device has resistive pull-downs (15K ohm) on both the D+ and D− signal lines. Typically a high/full-speed USB client device has a pull-up resistor (1.5K ohm) on the D+ line. A low-speed USB client device uses a pull-up resistor on the D− signal line. A high-speed USB client device uses a pull-up resistor on the D+ signal line. Part of the enumeration process for USB is deciding if the client is a high-speed device, full-speed device, or a low-speed device. When power is applied by the host device through the VBUS signal, the D+ and D− signals are either high/full speed or low-speed depending on the configuration of the pull-up resistor for the USB client device.
When the D+ signal is high (4.5V) and the D− is low, the speed of the USB client device is high/full speed (printer, scanner, etc.). When the D+ signal is low and the D− signal is high (4.5V), the speed of the USB client device is low (mouse, keyboard, etc.).
The following U.S. Patents, discussed below, are incorporated herein by reference: U.S. Pat. Nos. 5,767,844; 5,799,196; 5,844,086; 5,938,770; 6,000,042; 6,105,097; 6,128,743; 6,147,682; 6,170,062; 6,175,530; 6,189,040; and 6,205,502.
U.S. Pat. No. 5,767,844 discloses a modified USB interface for allowing remote power up of a computer while permitting normal remote power down.
U.S. Pat. No. 5,799,196 discloses a system for powering a computer in sleep mode by a USB device via a USB port (see especially claims 6 and 12; see also claims 7-10).
U.S. Pat. No. 5,844,086 discloses a system in which non-standard voltages can be supplied through a USB cable to a USB client device.
U.S. Pat. No. 5,938,770 discloses a computer monitor which has USB ports and can supply power to USB devices connected thereto.
U.S. Pat. No. 6,000,042 discloses a USB controller with a fault detection circuit.
U.S. Pat. No. 6,105,097 discloses a system for interconnecting USB devices (such as two computers) and managing the power consumed by each.
U.S. Pat. No. 6,128,743 discloses a USB hub for interconnecting multiple USB devices with a USB host. The USB hub can be powered by the host or with its own power supply.
U.S. Pat. No. 6,147,682 is similar to U.S. Pat. No. 5,938,770 and discloses a computer monitor which has USB ports and can supply power to USB devices connected thereto.
U.S. Pat. No. 6,170,062 is a division of U.S. Pat. No. 6,000,042 and also discloses a USB controller with a fault detection circuit.
U.S. Pat. No. 6,175,530 discloses a system in which a low power condition on an FPGA interface device interconnecting a target FPGA device and host system is detected via a USB connection, and power is supplied to the FPGA interface device by the target FPGA device. However, the power is not supplied by the target FPGA device through a USB cable.
U.S. Pat. No. 6,189,040 discloses a data controller which interconnects a host computer with a plurality of client devices and directs transmission of data between the client devices.
U.S. Pat. No. 6,205,502 discloses a USB controller with a switch to allow multiple USB devices to be plugged into the controller and recognized by the USB host after flipping of the switch.